The present invention relates to electrorheological fluids, systems, and devices, in which the fluid contains a polar liquid activator. The distribution of the activator is modified by means of sorption in a solid polymer.
Electrorheological ("ER") fluids are fluids which can rapidly and reversibly vary their apparent viscosity in the presence of an applied electric field. ER fluids are generally dispersions of finely divided solids in hydrophobic, electrically non-conducting oils. They have the ability to change their flow characteristics, even to the point of becoming solid, when subjected to a sufficiently strong electrical field. When the field is removed, the fluids revert to their normal liquid state. ER fluids may be used in applications in which it is desired to control the transmission of forces by low electric power levels, for example, in clutches, hydraulic valves, shock absorbers, vibrators, or systems used for positioning and holding work pieces in position.
Numerous types of electrorheological fluids are known, many of which require water or some other polar activating liquid in order to exhibit significant activity. For example, PCT application WO93/14180, published Jul. 22, 1993, discloses an electrorheological fluid comprising a hydrophobic liquid phase, cellulosic particles as a dispersed phase and a functionalized polysiloxane. The fluid can further contain an organic polar compound, other than the material of the hydrophobic liquid phase.
European publication EP 0 432 601 A1, Herrmann et al., Jun. 19, 1991, discloses electroviscous fluids based on dispersed polyethers. The invention relates to electroviscous fluids, consisting essentially of (a) a linear and/or branched, optionally functionalized polyether or its monomer, the reaction product of such a polyether or monomer with mono-or oligofunctional compounds and, optionally further additional additives; (b) dispersing agents, and also (c) a nonaqueous dispersion medium. The dispersion medium can be silicone oil. The dispersed phase can be polyethylene glycol or trifunctional polyethylene glycol. The dispersing agent can be an .alpha.,.omega.-polyetherpolydimethyl siloxane copolymer. A crosslinking agent can be toluene diisocyanate or triacetoxymethylsilane. In a typical form of preparation of the EVF of the invention, the material that is to be introduced is mixed with the reactive additive or the crosslinking material. After homogenizing the components, the mixture is dispersed in a fluid phase containing the dispersant.
In another field of technology, certain polymeric gels are known to be able to reversibly absorb fluids under various conditions. For example, U.S. Pat. No. 5,100,933, Tanaka et al., Mar. 31, 1992, discloses collapsible gel compositions of ionized crosslinked polyacrylamide gels. They are capable of drastic volume changes in response to minor changes in solvent concentration, temperature, pH, or salt concentration of the solvent.